Every year millions of children are faced with the severe consequences associated with war and political conflict. Although it is well established that children exposed to war are at increased risk for the development of mental health problems, some children show remarkable psychological resilience. Vulnerability and resilience to war-related experiences have been associated with a variety of risk and protective factors across different levels of analysis including social, psychological, and biological factors. However, not much is known regarding the dynamic interplay between these factors, particularly how environmental factors interact with biological systems in the prediction of risk and resilience. The proposed research will advance the field by investigating the biological underpinnings of individual differences in refugee children's response to acute war-related trauma exposure. Applying a modern multilevel perspective, the study aims to explore the intricate interplay between psychosocial, neuroendocrine, epigenetic, and genetic factors in the prediction of risk and resilience related to the experience of war in 1,000 8-16 year old Syrian refugee children (and their primary caregivers) in Lebanon. Besides questionnaire and interview data, we will also collect cheek swabs (for DNA) and hair samples (for cortisol and other stress- related hormones) applying recruitment strategies that proved highly successful in a recent study conducted by the Lebanon-based collaborators. Overcoming limitations of existing work, we will take into account both maladaptive and adaptive outcomes in response to both risk and protective factors and investigate the development of resilience over the period of 12 months in a subsample of 650 children. The proposed interdisciplinary project includes research groups in the UK and Lebanon and has the following research aims: 1. Examine epigenetic, endocrine, and genetic differences between resilient and vulnerable children 2. Investigate genetic moderation of trauma exposure (gene-environment interaction) 3. Examine associations between environmental factors and genome-wide DNA methylation 4. Investigate the effects of protective factors on adaptive outcomes 5. Examine the development of refugee children's psychological resilience over time. A better understanding of how social, psychological, and biological factors contribute to the mental health of refugee children will be important in order t better protect war-affected children from the negative effects of political conflict and displacement and to promote their psychological resilience. In addition, the proposed project will elucidate more generally how environmental influences get under the skin, particularly, how risk and protective factors exert their effects on psychological outcomes through biological pathways and processes.